Client computing devices may be used to request content pages and other network-accessible content from content servers. In some cases, information identifying or otherwise associated with a user of the client device may be transmitted with a content request to the server. For example, a small file known as a cookie may have been previously sent to the client device in response to a content request. The cookie may include demographic, tracking, or identifying information. When the client device makes a subsequent content request to the server, the cookie may be transmitted with the content request, and the server can use the data in the cookie to determine the identity of the user, demographic information about the user, which content requests the user has previously made, etc. Content providers may use such data to provide more relevant content to users.
In many cases, a content request takes the form of a Hypertext Transfer Protocol (HTTP) request including a network address of the requested content, such as a Uniform Resource Locator (URL). Identifying information may be appended to the end of the URL as a query string. In addition, data such as the Internet Protocol (IP) address of the client device may be made available to the server when a connection is established, and data about various components of the client device may be embedded into the request itself. Such data may provide content providers with information that can be used to identify users and to track content requests made by users.
Proxy servers and other intermediary systems may be used to block cookies, obfuscate IP addresses, and the like. In a typical implementation, a content request from a client device is first routed through the proxy server, which processes the request and forwards it on to the content server. In some cases, the proxy server can create accounts with content servers and utilize those accounts when requesting content on behalf of client devices, thereby shielding the actual identity or demographics of users while still allowing content providers to tailor content to the users based on the accounts created by the proxy.